Enhanced Electrocatalytic Activity of Pt/3D Hierarchical Bimodal Macroporous Carbon Nanospheres

Macroporous Structures of Nb-SnO2 Particles as a Catalyst Support Induce High Porosity and Performance in Polymer Electrolyte Fuel Cell Catalyst Layers

Macroporous niobium-doped tin oxide (NTO) is introduced as a robust alternative to conventional carbon-based catalyst supports to improve the durability and performance of polymer electrolyte fuel cells (PEFCs). Metal oxides like NTO are more stable than carbon under PEFC operational conditions, but they can compromise gas diffusion and water management because of their denser structures. To address this tradeoff, we synthesized macroporous NTO particles using a flame-assisted spray-drying technique employing poly(methyl methacrylate) as a templating agent. X-ray diffraction analysis and scanning electron microscopy confirmed the preservation of crystallinity and revealed a macroporous morphology with larger pore volumes and diameters than those in flame-made NTO nanoparticles, as revealed by mercury porosimetry. The macroporous NTO particles exhibited enhanced maximum current density and reduced gas diffusion resistance relative to commercial carbon supports. Our findings establish a foundation for integrating macroporous NTO structures into PEFCs to optimize durability and performance.

Controllable Synthesis of Porous and Hollow Nanostructured Catalyst Particles and Their Soot Oxidation

The introduction of macroporous structures into three-way catalysts (TWCs) through polymer template-assisted spray drying has attracted attention because of its enhanced gas diffusion and catalytic performance. However, the surface charge effect of polymeric template components has not been investigated to control the structure of the TWC particles during synthesis. Thus, this study investigated the effect of template surface charges on the self-assembly behavior of TWC nanoparticles (NPs) during drying. The self-assembly of TWC NPs and polymer particles with different charges produced a hollow structure, whereas using the same charges generated a porous one. Consequently, the mechanism of particle self-assembly during drying and final structure particle formation is proposed in this study. Here, porous TWC particles demonstrated a faster oxidation of soot particles than that of hollow-structured particles. This occurred as a result of the larger contact area between the catalyst surface and the solid reactant. Our findings propose a fundamental self-assembly mechanism for the formation of different TWC structures, thereby enhancing soot oxidation performance using macroporous structures.

Multifunctional, Hybrid Materials Design via Spray-Drying: Much more than Just Drying

Spray-drying is a popular and well-known "drying tool" for engineers. This perspective highlights that, beyond this application, spray-drying is a very interesting and powerful tool for materials chemists to enable the design of multifunctional and hybrid materials. Upon spray-drying, the confined space of a liquid droplet is narrowed down, and its ingredients are forced together upon "falling dry." As  detailed in this article, this enables the following material formation strategies either individually or even in combination: nanoparticles and/or molecules can be assembled; precipitation reactions as well as chemical syntheses can be performed; and templated materials can be designed. Beyond this, fragile moieties can be processed, or "precursor materials" be prepared. Post-treatment of spray-dried objects eventually enables the next level in the design of complex materials. Using spray-drying to design (particulate) materials comes with many advantages-but also with many challenges-all of which are outlined here. It is believed that multifunctional, hybrid materials, made via spray-drying, enable very unique property combinations that are particularly highly promising in myriad applications-of which catalysis, diagnostics, purification, storage, and information are highlighted.

Pt-C interactions in carbon-supported Pt-based electrocatalysts

Carbon-supported Pt-based materials are highly promising electrocatalysts. The carbon support plays an important role in the Pt-based catalysts by remarkably influencing the growth, particle size, morphology, dispersion, electronic structure, physiochemical property and function of Pt. This review summarizes recent progress made in the development of carbon-supported Pt-based catalysts, with special emphasis being given to how activity and stability enhancements are related to Pt-C interactions in various carbon supports, including porous carbon, heteroatom doped carbon, carbon-based binary support, and their corresponding electrocatalytic applications. Finally, the current challenges and future prospects in the development of carbon-supported Pt-based catalysts are discussed.

Batch synthesis of high activity and durability carbon supported platinum catalysts for oxygen reduction reaction using a new facile continuous microwave pipeline technology

Traditional synthesis methodologies for fuel cell catalyst production involve long reactions and uncontrollable reaction processes. Synthesis methods for the production of catalysts typically have difficulties to achieve catalysts materials with consistency, high activity, and durability. In this study, a fast, simple, and suitable continuous pipeline microwave method for catalyst mass production was developed, with the carbon carrier being treated at different temperatures simultaneously. The method herein developed resulted in carbon-supported platinum (Pt) catalysts with high activity and high durability. In addition, the half-wave potential of the catalyst exceeded 0.9 V, the electrochemical active surface area reached 85.7 m²-g_Pt^-1, and the mass specific activity reached 171.1 mA-mg^-1. Remarkably, after 30,000 cycles of Pt attenuation tests and 30,000 cycles of carbon carrier attenuation tests, the retention rate of the annealed carbon carrier catalyst reached 80 %. As a membrane electrode, the catalyst generated a single cell maximum power density of 1.4 W-cm^-2, and the Pt content reached 0.286 g_Pt-kW^-1. The work provides an effective and practical method for the mass production of high-performance and high-durability catalysts, which guiding significance for mass production of catalysts.

Enhanced Protein Adsorption Capacity of Macroporous Pectin Particles with High Specific Surface Area and an Interconnected Pore Network

There has been much interest in developing protein adsorbents using nanostructured particles, which can be engineered porous materials with fine control of the surface and pore structures. A significant challenge in designing porous adsorbents is the high percentage of available binding sites in the pores owing to their large surface areas and interconnected pore networks. In this study, continuing the idea of using porous materials derived from natural polymers toward the goal of sustainable development, porous pectin particles are reported. The template-assisted spray drying method using calcium carbonate (CaCO₃) as a template for pore formation was applied to prepare porous pectin particles. The specific surface area was controlled from 177.0 to 222.3 m² g^-1 by adjusting the CaCO₃ concentration. In addition, the effects of a macroporous structure, the specific surface area, and an interconnected pore network on the protein (lysozyme) adsorption capacity and adsorption mechanism were investigated. All porous pectin particles performed rapid adsorption (∼65% total capacity within 5 min) and high adsorption capacity, increasing from 1543 to the highest value of 2621 mg g^-1. The results are attributed to the high percentage of available binding sites located in the macropores owing to their large surface areas and interconnected pore networks. The macroporous particles obtained in this study showed a higher adsorption capacity (2621 mg g^-1) for lysozyme than other adsorbents. Moreover, the rapid uptake and high performance of this material show its potential as an advanced adsorbent for various macromolecules in the food and pharmaceutical fields.

A facile synthesis of hierarchically porous graphene for high-performance lithium storage

Hierarchically porous graphene with macro-mesopores is highly desired for enhancing lithium storage.

Anchored Pt-Co Nanoparticles on Honeycombed Graphene as Highly Durable Catalysts for the Oxygen Reduction Reaction

Durability is an important factor in evaluating the performance of a catalyst. In this work, the spatial protection of the carrier to nanoparticles was considered to improve the durability of the catalyst. It is found that a honeycombed graphene with a three-dimensional (3D)-hierarchical porous structure (3D HPG) can help to reduce the shedding of Pt-Co nanoparticles (Pt-Co NPs) because 3D HPG can form a protective layer to reduce the direct erosion of Pt-Co NPs on the interface by an electrolyte. Then, appropriate oxygen groups were introduced on the 3D reduced hierarchical porous graphene oxide (3D rHPGO) to improve the dispersion of Pt-Co NPs on the surface of the carrier. It was found that the Pt d-band of the catalyst was anchored by π sites of carbonyl of an oxygen group. After optimization, the catalyst (referred to as Pt-Co/3D rHPGO) achieved a 2-fold enhancement in mass activity than that of a commercial Pt/C catalyst. More importantly, after the accelerated durability test (ADT) of 20 000 cycles, the Pt-Co/3D rHPGO catalyst can almost sustain this level of performance, whereas other catalysts showed a comparatively large loss of activity. According to the results, the high durability of Pt-Co/3D rHPGO was attributed to spatial protection of Pt-Co NPs and the defects on the surface allowed the electrolyte to enter. In addition, oxygen groups provided an anchoring effect on nanoparticles. Thus, the Pt-Co/3D rHPGO electrocatalyst exhibited splendid durability, holding a potential to be applied in PEMFC for long-term work.

Controllable synthesis of spherical carbon particles transition from dense to hollow structure derived from Kraft lignin

The tailored synthesis of carbon particles with controllable shapes and structures from biomass as a raw material would be highly beneficial to meet the demands of various applications of carbon materials from the viewpoint of sustainable development goals. In this work, the spherical carbon particles were successfully synthesized through a spray drying method followed by the carbonization process, using Kraft lignin as the carbon source and potassium hydroxide (KOH) as the activation agent. As the results, the proposed method successfully controlled the shape and structure of the carbon particles from dense to hollow by adjusting the KOH concentration. Especially, this study represents the first demonstration that KOH plays a crucial role in the formation of particles with good sphericity and dense structures. In addition, to obtain an in-depth understanding of the particle formation of carbon particles, a possible mechanism is also investigated in this article. The resulting spherical carbon particles exhibited dense structures with a specific surface area (1233 m²g^-1) and tap density (1.46 g cm^-3) superior to those of irregular shape carbon particles.

Controllable Synthesis of Carbon-Coated SiOx Particles through a Simultaneous Reaction between the Hydrolysis-Condensation of Tetramethyl Orthosilicate and the Polymerization of 3-Aminophenol

Core-shell particles are desirable for many applications, but the precise design and control of their structure remains a great challenge. In this work, we developed a strategy to fabricate carbon-coated SiO_x (SiO_x@C) core-shell particles via a sol-gel method using the simultaneous hydrolysis-condensation of tetramethyl orthosilicate (TMOS), the polymerization of 3-aminophenol and formaldehyde in the presence of ammonia as a basic catalyst, and cetyltrimethylammonium bromide (CTAB) as a cationic surfactant in the mixed solution of water and methanol followed by the carbonization process. Results from this study provide new insight into the design of core-shell particles by using TMOS as an effective silica precursor for the first time with a well-controlled reaction rate and spherical morphology. To obtain an in-depth understanding of the formation of core-shell structure, a possible mechanism is also proposed in this article. When tested as an anode material for lithium ion batteries (LIBs), the obtained SiO_x@C particles delivered a reversible capacity of 509.2 mAh g^-1 at a current density of 100 mA g^-1. This electrochemical performance is significantly better than those of similar composites without the core-shell structure. The capacity retention after 100 cycles was approximately 80%. These results suggest great promise for the proposed SiO_x@C particles with core-shell structure, which may have potential applications in the improvement of various energy-storage materials.

Triple phase boundary and power density enhancement in PEMFCs of a Pt/C electrode with double catalyst layers

Exploring efficient approaches to design electrodes for proton exchange membrane fuel cells (PEMFCs) is of great advantage to overcome the current limitations of the standard platinum supported carbon (Pt/C) catalyst. Herein, a Pt/C electrode consisting of double catalyst layers (DCL) with low Pt loading of around 0.130 mgPt cm-2 is prepared using spray and electrophoresis (EPD) methods. The DCL electrode demonstrated a higher electrochemical surface area (ECSA-52.5 m2 gPt -1) and smaller internal resistance (133 Ω) as compared to single catalyst layer (SCL) sprayed (37.1 m2 gPt -1 and 184 Ω) or EPD (42.4 m2 gPt -1 and 170 Ω) electrodes. In addition, the corresponding DCL membrane electrode assembly (MEA), which consists of a Pt/C DCL electrode at the anode side and a Pt/C sprayed electrode at the cathode side, also showed improved PEMFC performance as compared to others. Specifically, the DCL MEA generated the highest power density of 4.9 W mgPt -1, whereas, the SCL MEAs only produced 3.1 and 3.8 W mgPt -1, respectively. The superior utilization of the Pt catalysts into the DCL MEA can originate from the enrichment of the triple phase boundary (TPB) presented on the Pt/C DCL electrode, which can strongly promote the adsorbed hydrogen intermediates' removal from the anode side, thus improving the overall PEMFC performance.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion

This review provides insight into various nanostructures designed by spray pyrolysis and their applications in energy storage and conversion.

Tailoring porous carbon spheres for supercapacitors

The last decade has witnessed significant breakthroughs in the synthesis of porous carbon spheres (PCSs). This Review provides an updated summarization on the controlled synthesis of PCSs for supercapacitors. The synthetic methodologies can be generally categorized into (i) hard templating, (ii) soft templating, (iii) the modified Stöber method, (iv) hydrothermal carbonization (HTC), and (v) aerosol-assisted methods. The obtained PCSs include microporous/mesoporous/macroporous carbon spheres, single-/multi-shelled hollow carbon spheres, and yolk@shell carbon spheres. The structure-electrochemical performance correlation is discussed. Finally, the future research directions on the rational design of PCSs for supercapacitors are predicted.